A ∼ 90° Late Silurian–Early Devonian apparent polar wander loop: The latest inertial interchange of planet earth?

Although rates of true polar wander have been small during the last 200 Myr of geological time primarily due to the slow response of the viscous lower mantle, it is possible for the Earthʹs rotation axis to move rapidly to the equator if mass perturbations within the interior cause the maximum and intermediate inertial axes to cross. Rotation of the silicate Earth is then recorded by a ∼ 90° arcuate sequence of palaeomagnetic poles embracing a time interval of < 20 Myr. An apparent polar wander loop (APW) of this length and duration is recorded by Silurian–Devonian palaeomagnetic data from two separated regions (the Caledonides and Gondwana) and is suggested by less well-constrained results from other continental blocks. The Caledonian and Gondwana data appear to identify a short term interchange of the Earthʹs inertial axes during the interval ∼ 410–390 Ma and yield a conventional continental reconstruction highlighting pending collision between Laurentia and the western margin of Gondwana near the Silurian–Devonian boundary to isolate the Rheic Ocean. This APW loop was accompanied by the extinction of successive oceans and occurred during, or shortly before, continental collisions between Gondwana, Laurentia, Baltica and Siberia to form the bulk of the supercontinent Pangaea. The implied rapid translation of the outer Earth resulting from transient modification of the Earthʹs figure is therefore most plausibly related to the avalanching of long lithosphere slabs into the lower mantle. The inertial interchange appears to be recorded by contemporaneous sea level changes although more refined stratigraphic data are required to confirm this.